3D printed beam mount .049 backplate

What size thread did you use to cut the AP Wasp carb?
Did it require any reduction first?

Good to see you are using socket head bolts too,
easy to adjust just the right amount of torque.

I use socket head wood screws for the beam mounts the hole
size you currently use is a bit big / smaller hole would help on
strength / splitting / cracks.

65 deg carb mount with a KB .049
Tatone Muffler with Larry's metal mounts.
Will bench test with a APC 4.6 x 3

Hex head inpoint stud bolt with locking nut.
Much lower weight compared to long bolt / spinner.
The thick beveled washer seats into the prop hubs
recess for improved alignment.

Basswood, the version I have to test has a carbon blend to it.

Killer Bee .049 with 3D Printed Backplate for RC Carb 65 deg.
Testing with muffler and exhaust deflector made reasonable
power considering not open exhaust / very easy on the ears.
SPI engine seemed to breath reasonably for bench testing.

APC 4.6x3 / 20,914 rpm peak / 60 mph pitch speed / 8.9oz thrust.
Stop screw needs to be set for low idle looks like it can handle 6.8k
with a larger prop much lower perhaps 5k I would expect.
25% nitro / 20% castor / 3 shims Cox High Compression Plug.

Engine ran well side mounted the exhaust system may have helped
with the steady running. Butter on the ears will make a great RC
engine project as is or open exhaust for full power. Aluminum mounting
brackets for bench testing ease and to acquire side mounting test.
3D mount was clean no air leaks great design for fuss free use!
Improved 65 deg. angle made access a breeze with the RC carb.



Absolutely zero vibrations with this set up very pleased with the low weight centered stud / nut method.
The engine did great with the bulky robust combat prop.

 

It all starts with a perfectly centered prop. I use fuel tube that
is a snug fit when the stud bolt went thru it sets the stage for
a centered prop. The trick is not to mess it up with a spinner
that slides / kicks out of center when tighten. Threaded bullet
spinners work great. The nut and stud method worked very
well today low mass tucked up close to the prop hub is another
factor to help reduce vibrations. I used a small crescent wrench
to tighten the locking nut no fear of stripping the threads. I put
about 6-7 lbs of torque on the nut.

Thank you Andras, have a few of these backplates and thus far the ones with RC
carbs on them have held up well with the locking nut. None have gotten loose on
me / no air leaks observed. Fuel draw has been good although if I use a muffler
I tend to go with a pressure tap to improve steady top end rpm.